If you’re an executive or board member with a tons of shares you make millions and can retire immediately (or at least after the transition you agree to is complete.)
But the price doesn't plummet when an attempt to acquire a company is announced.
The price plummets when the holders of many shares want to sell. An attempted acquisition is the opposite of that situation.
The share price is for the current share supply. If the supply increases, then the price goes down.
There is also a confounding effect in the cases where shares have actually flooded the market, where the confounder is whatever the reason for flooding is. But even if you magically forced a mass sale with no negative event causing it, the price would still plummet due to the supply flood.